Direct mix receiver

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The direct mixing receiver , or homodyne receiver , is a heterodyne receiver with an oscillator frequency that corresponds to the reception frequency ω. From a technical point of view, it is a synchronous demodulator or lock-in amplifier .

The mixture with the oscillator frequency in this case leads directly to the low-frequency signal. The gain and selection (see selectivity ) of the desired signal carried in the low-frequency amplifier. There is no IF amplifier. In contrast to the superheterodyne receiver , with this reception technique the mirror spectra are avoided by the formation of the complex envelope. The formation of the complex envelope results in complex signals in the baseband which consist of a real and an imaginary component, which are also referred to as I and Q components.

In general, with this receiver structure, the high-frequency received signal is subjected to a Hilbert transformation and an analytical signal is thus formed. This is multiplied by the complex carrier frequency e −jωt in order to obtain the complex baseband signal directly. Alternatively, and equivalent to this, the received signal can also first be multiplied by the complex carrier frequency, and then the baseband signal is obtained in the form of two exactly identical low-pass filters for the real or imaginary part.

Direct-mixing receiver structures represent the predominant receiver structure in digital transmissions in the field of digital signal processing . This receiver structure is common especially in digital modulation methods with high spectral efficiency such as quadrature amplitude modulation .

In conventional analog receiver circuits, on the other hand, the homodyne receiver only plays a subordinate role, since it is difficult to implement in terms of circuitry due to the limited accuracy of electronic components and is complex in terms of circuitry. In particular, the implementation of analog Hilbert transformers or precisely matched low-pass filters limit the practically usable use. Adapted analog direct mix receivers have been used in part in the amateur radio sector.

See also

swell

  1. ↑ Amateur radio, A handbook for radio amateurs, edited by Karl-Heinz-Schubert, Military Publishing House of the German Democratic Republic, Berlin, 1956/1978

literature

  • Karl-Dirk Kammeyer: communications engineering . 4th edition. Vieweg + Teubner, 2008, ISBN 978-3-8351-0179-1 .